The objective of this work is to characterize the sites of substrate attachment and catalysis in succinic thiokinases of Escherichia coli and porcine heart with respect to their proximity and loci on the alpha and beta chains of these proteins. Also of interest is the molecular basis of succinate activation of acetate kinase from Veillonella alcalescens. BIBLIOGRAPHIC REFERENCE: Nishimura, J.S., Petrich, J.A., Milne, A.F., and Mitchell, T. (1977) N,N'-o-Phenylenedi(1,4-14C)maleimide. Its synthesis and application in the cross-linking of Escherichia coli succinic thiokinase. Int. J. Biochem., in press.